[llvm] [X86][SelectionDAG] Fix the Gather's base and index by modifying the Scale value (PR #137813)

[Rohit Aggarwal via llvm-commits]

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@@ -56604,11 +56640,25 @@ static SDValue combineGatherScatter(SDNode *N, SelectionDAG &DAG,
         Index = DAG.getNode(ISD::TRUNCATE, DL, NewVT, Index);
         return rebuildGatherScatter(GorS, Index, Base, Scale, DAG);
       }
+
+      // Shrink if we remove an illegal type.
+      if (!TLI.isTypeLegal(Index.getValueType()) && TLI.isTypeLegal(NewVT)) {
+        Index = DAG.getNode(ISD::TRUNCATE, DL, NewVT, Index);
+        return rebuildGatherScatter(GorS, Index, Base, Scale, DAG);
+      }
     }
   }
 
   EVT PtrVT = TLI.getPointerTy(DAG.getDataLayout());
 
+  // if (Index.getOpcode() == ISD::SHL) {
+  //   unsigned BitWidth = Index.getScalarValueSizeInBits();
+  //   unsigned MaskBits = BitWidth - Log2_32(Scale->getAsZExtVal());
+  //   APInt DemandedBits = APInt::getLowBitsSet(BitWidth, MaskBits);
+  //   if (TLI.SimplifyDemandedBits(Index, DemandedBits, DCI)) {
+  //     return SDValue(N, 0);
+  //   }
+  // }
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rohitaggarwal007 wrote:

Done

https://github.com/llvm/llvm-project/pull/137813